In some prior art vapor-compression refrigeration systems, a condenser thereof is positioned outdoors, to take advantage of relatively low ambient temperatures. When the ambient temperature is relatively low, advantageously, heat dissipation from the condenser is aided by the relatively low ambient temperature. In these circumstances, within a range of ambient temperatures, there is a direct relationship between the ambient temperature at the condenser and the efficiency of the system overall: the colder the ambient temperature, the lower the condenser head pressure, and the more efficiently the system operates.
A typical condenser unit 20 of the prior art is schematically illustrated in FIG. 1. As can be seen in FIG. 1, the prior art condenser unit 20 typically includes a compressor 22, a condenser 24, a condenser fan 26 for directing air through or over the condenser 24 to cool the refrigerant therein (not shown), and it may also include a liquid receiver 54. As is well known in the art, the condenser unit is included in a vapor-compression system, e.g., used for refrigeration. In the refrigeration system, the refrigerant is circulatable through an evaporator (not shown in FIG. 1), which is in fluid communication with a substantially closed controlled space. The refrigerant is circulatable through the evaporator for heat transfer from air in the controlled space to the refrigerant, as is known.
Refrigerant vapor is pumped from the evaporator to the compressor 22, and the superheated vapor discharged from the compressor 22 is directed to the condenser 24, where the refrigerant condenses. Often, the condenser 24 may be located outside the building in which the controlled space is located, i.e., the condenser is located in an uncontrolled space. Heat given off on condensation of the refrigerant in the condenser is dissipated to the atmosphere, and the liquid refrigerant is directed from the condenser 24 to the liquid receiver 54, which contains a reservoir of the liquid refrigerant. The condenser fan 26 aids in the dissipation of heat to the atmosphere. From the liquid receiver 54, the liquid refrigerant is drawn toward the expansion valve (not shown) of the system.
As is well known in the art, proper operation of the system requires a minimum pressure difference across the expansion valve. However, in the prior art condenser unit as illustrated in FIG. 1, fluctuations in the ambient temperature in the uncontrolled space result in fluctuations in the compressor discharge (or head) pressure, adversely affecting efficiency, and the performance of the system overall. When the ambient temperature is very low, the head pressure could become so low that the system does not function properly.
In the prior art, the problem of fluctuations in the ambient temperature is typically addressed by using a flooding valve. A prior art condenser unit 120 is schematically illustrated in FIG. 2. (As will be described, the remainder of the drawings illustrate the present invention.)
The condenser unit 120 typically includes a compressor 122, a condenser 124, a condenser fan 126, and a liquid receiver 154 (FIG. 2). However, as can be seen in FIG. 2, the condenser unit 120 also includes a flooding valve 130. The flooding valve 130 is positioned to control the flow of liquid refrigerant from the condenser 124.
As is well known in the art, the flooding valve causes liquid refrigerant to back up into (i.e., flood) the condenser, when the head pressure falls below a preselected head pressure. Because flooding the condenser limits the surface area inside the condenser on which the refrigerant may condense, the flooding results in an increase in condensing pressure, i.e., head pressure.
As illustrated in FIG. 2, the prior art condenser unit 120 typically also includes a bypass valve 132. The bypass valve 132 is provided because the flooding valve reduces the flow of refrigerant to the receiver. The bypass valve 132 permits the superheated refrigerant vapor to bypass the condenser when a predetermined pressure difference between the compressor's discharge line and the receiver exists.
However, there are some disadvantages to the prior art solutions intended to address fluctuating ambient temperatures at the condenser that affect the refrigerant head pressure. For instance, the flooding valve, in effect, requires the compressor to function at an artificially high level (i.e., energy consumption by the compressor is greater than it otherwise would have been). Also, because of the flooding valve, significantly more liquid refrigerant is required to be added to the system. This is undesirable for two reasons. First, adding more refrigerant results in additional costs, due to the cost of the additional refrigerant. Second, due to issues involving the environmental impact of refrigerants, it is generally thought to be desirable to decrease refrigerant volume requirements.